ldb bug fixes

[Adrian Cochrane]

Since the symptoms of the big I fixed in more previous patch were 
incorrect, here's a patch which corrects the error propagation in LDB.

On Wed, Dec 2, 2015 at 4:31 PM, Adrian Cochrane 
<adrianc at catalyst.net.nz> wrote:
> Another update, realized that if I'm allocating empty arrays it's 
> probably useful still to check it for null.
> 
> On Thu, Nov 26, 2015 at 4:45 PM, Adrian Cochrane 
> <adrianc at catalyst.net.nz> wrote:
>> Updated patch per Andrew's comments.
>> 
>> On Wed, Nov 25, 2015 at 10:56 AM, Andrew Bartlett 
>> <abartlet at samba.org> wrote:
>>> On Mon, 2015-11-23 at 14:35 +1300, Adrian Cochrane wrote:
>>>>  It turns out that wouldn't be an easier fix because
>>>>  /lib/talloc/talloc_guide.txt specifically states:
>>>>  >   talloc_realloc(context, ptr, type, 0) ==> talloc_free(ptr);
>>>> 
>>>>  However I did take your advice and incorporated it into this 
>>>> updated
>>>>  patch.
>>> 
>>> I think this, but with an error check on
>>> msg->elements = talloc_array(msg, struct ldb_message_element, 0);
>>> 
>>> would be the correct solution.
>>> 
>>> LDB entries with zero attributes are vanishingly rare, but asking 
>>> for
>>> zero attributes is common, as is asking only for attributes that 
>>> don't
>>> exist.  We may post-process the ldb_message to add a generated
>>> attribute later, and we should have a zero-length array to do that 
>>> on.
>>> 
>>> This also follows the principle of least supprise from the current
>>> code, which always returned an array the same length as the database
>>> object (ie, always non-NULL, even with num_elements == 0)
>>> 
>>> Thanks,
>>> 
>>> Andrew Bartlett
>>> 
>>> --
>>> Andrew Bartlett
>>> https://samba.org/~abartlet/
>>> Authentication Developer, Samba Team         https://samba.org
>>> Samba Development and Support, Catalyst IT
>>> https://catalyst.net.nz/services/samba
>>> 
>>> 
>>> 
>>> 
>>> 
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